1. Field of the Invention
The present invention pertains to coatings for use on electrical conduits, water supply lines, and structural materials, which are flexible, adherent, and when exposed to high temperatures, expand to form an insulative yet coherent coating. The invention further pertains to articles coated with the inventive coating, both pre- and post-installation.
2. Description of the Related Art
A significant contributing cause to the destruction of buildings and other structures by fire is damage to structural, utilitarian, and life safety components. Intense heat generated by fire and/or explosion can severely weaken structural steel, contributing to building collapse. This effect is believed to have been a significant factor in the collapse of the World Trade Center towers in September of 2001. It would be desirable to minimize damage to such structural components. However, minimizing damage to utilitarian and life safety components such as water supply lines for fire sprinkler systems and electrical conduits is also of paramount importance.
Damage to water lines which supply fire sprinkler systems results in the inability of such systems to work for their intended purpose. Damage to electrical systems not only opens up the possibility of additional incendiary sources caused by shorting of electrical cables encased in conduit, but also destroys communication capabilities and emergency power sources, which then may lead to increased personal injury and loss of life. The larger the structure, the more important it becomes to minimize damage to all components.
In the past, structural steel has often been covered with insulative material containing inorganic binders. This material has conventionally been rather thick, and once cured in place, is relatively inflexible. The binder systems used often deteriorate with age, or due to inadequate adhesion to the substrate, cause the material to fall away from the substrate, particularly in tall buildings where appreciable movement and/or bending of the components is expected. The binder systems employed also make the insulative material susceptible to being easily destroyed upon impact. For example, examination of the World Trade Center prior to the incident leading to its collapse showed large portions of structure which had once been coated with insulation to be substantially free of such insulation (missing). The remaining insulation was instantly destroyed by impact or the subsequent inferno. The same type of insulation materials have been used for water lines, with similar problems.
Electrical conduit poses unique problems, in particular because use of electrical conduit in buildings and infrastructure is extensive, and because conduit is frequently bent to conform to routing requirements. In the past, both structural and utilitarian building components have only been covered by insulation after installation. Post-installation covering is mandated both by the thickness and lack of durability of prior insulation systems as well as the inability of such systems to survive bending operations.
Durable insulation systems have generally been used only for noise attenuation or thermal insulation, i.e. to decrease heat flow to the surroundings from hot conveying lines, and have also suffered from a lack of insulation efficiency or high cost. For example, in U.S. Pat. No. 3,875,971, ceramic coated metal articles are disclosed. These articles are produced by adhering zirconia in the form of powder, fiber, tape, or woven material to metal by means of a ceramic enamel. However, such articles are relatively expensive, and cannot withstand bending operations.
In U.S. Pat. No. 6,338,366, pipe insulation in the form of a thin sleeve secured by strap-type clamps is disclosed. However, such insulation must be applied post-installation, and cannot be applied to structural steel without unique and expensive clamping means. Similar jacketed insulation has been used for many years on steam pipes. Such insulation is not intended for resistance to fire.
U.S. Pat. No. 5,400,830 discloses a vehicle exhaust pipe which appears to be deformable, comprising an inner metal pipe, a layer of ceramic insulating material, and a surrounding jacket of a high temperature-resistant thermoplastic. The result is a relatively bulky structure due to the thickness of the insulative layer required to prevent damage to the thermoplastic exterior. Further, the high temperature thermoplastic material is relatively expensive. Such products are designed to keep heat within, for example to provide for more rapid light-off in catalytic converters. If exposed to high temperature from the outside, even the high melt thermoplastics would be rapidly destroyed.
It would be desirable to provide a fire protective insulative system which is relatively inexpensive, which is non-bulky, which is highly adherent, which can be applied either pre- or post-installation, and which is capable of being deformed such that components such as electrical conduit can be supplied already coated with the insulative system and bent employing conventional bending tools without causing loss of the insulation system.
It would be further desirable to provide a flexible fire protection insulative system which when exposed to fire forms a char which protects and insulates the substrate, i.e. structural members, utilities, power and communications lines, etc., from fire damage.
It would be further desirable to provide an insulation system which is substantially non-toxic, which employs little or no volatile organic solvents, and which liberates few toxic byproducts when exposed to high temperature.